Eastern European broadleaved forests north of the 50th degree of latitude serve as a core breeding area for most migratory bat species wintering in Eastern and Central Europe. The southern border of this region has faced an increase in clear-cutting intensity in recent decades. We conducted a standardized mist-netting survey on eleven heterogeneous oak forest plots in order to assess how land cover types and forest age affect abundance, diversity and the breeding of bats. We found that abundance indices and species richness increased from upland plots surrounded by agricultural lands to riverine or waterside plots with high forest cover. Particularly large mature forests older than 90 years positively affected the breeding activity of bats, their abundance indices and overall species richness. Regarding species associations with specific habitats, we found that Myotis brandtii, Nyctalus leisleri and Pipistrellus pygmaeus were mainly found in mature deciduous forest stands, while Plecotus auritus appeared to be the only species tolerating clearcuts and young stands. Forest-dwelling species such as Nyctalus noctula and Pipistrellus nathusii were additionally associated with water habitats. Thus, the combination of mature forests and water sources is essential in shaping Eastern European assemblages of forest bat species.

Capsule: Tawny Owls Strix aluco used a wide variety of tree holes for roosting, but only a minority were used for nesting, which comprised those holes at greater heights in larger trees and with a flat base. Aims: We aimed to determine the type and dimensions of tree holes used by Tawny Owls for roosting and nesting, including which tree species were the most important hole providers, and the density of tree holes available for Tawny Owls in forests of different age classes. Methods: We conducted visual searches for all large tree holes within study plots, recorded their measurements and signs of use, comparing the features of used and unused holes. Data were collected in medium-aged and old-growth forests (Ukraine, Homilsha Forest, 750 ha, 10 seasons) and in primeval forest (Poland, Białowieża Forest, 150 ha, 2 seasons). Results: Roosting holes came in a wide variety of shapes and sizes, frequently being very deep and with an uneven base. Hole entrances needed to be over 10 cm wide and the hollows more than 20 cm deep, presumably to enable owls to enter and evade predators. All nesting holes had a flat base and were located in larger trees, at greater heights than roosting holes. Old trees of low commercial timber value (European Hornbeam Carpinus betulus, Small-leaved Lime Tilia cordata, European Pear Pyrus communis) were the most important hole providers. Suitable holes were found in trees of at least 80 years old, and their abundance increased with tree age, exceeding 50 holes/km² in the primeval forest. Conclusion: Despite the abundance of suitable roosting holes, nesting holes remained a rare resource associated with larger, older trees. As tree species of low economic value were the main hole providers, these should be retained in forestry operations.

Tree cavities offer protected shelters and resources for arboreal vertebrates worldwide. In general, cavities with larger openings are better accessible for predators and are avoided by smaller species for breeding, but can still be attractive for occasional use. The current study explores the diversity of functional use types and species interactions at the largest available tree cavities (entrance width ≥ 10 cm) in a temperate European forest with a low number of large cavity‐breeding species. Year‐round camera observations at 9 cavities (range 0.7–3.5 years) revealed 34 visiting species of birds and mammals, including non‐cavity‐breeding species. The top predator threatening other large‐cavity users was European pine marten ( Martes martes ), which regularly visited each cavity year‐round, on average every 0.7 months. Tawny owl ( Strix aluco ) was the only species successfully breeding in cavities, arguably because of its ability to defend the nests. However, other species visited cavities at an average rate of 1.5 visits per day, making predominantly short visits (less than 30 s) interpreted as exploration, searching for food, or inspecting for the presence of owls (mobbing). Making short visits and time segregation with predators was a behavioural strategy to exploit cavities for most species. These results confirm that, similarly to other keystone structures (large arboreal nests, ground burrows, etc.), large tree cavities attract a significant part of the arboreal vertebrate community and enrich their habitats. To sustain these functions in wooded ecosystems, management should provide a surplus of available cavities and diversity of their characteristics even when the apparent number of breeding species is low.

The Tawny owl (Strix aluco) is a common owl species in Europe, demonstrating generalist diet strategy. Its main prey are small rodents and numerous studies show that the composition of its diet broadly reflects changes in prey species abundance in its habitats. Due to strictly sedentary habits of adult birds and their year-round territoriality, it is possible to locate habitats of their prey with a precision of several hundred metres. Analysis of owl pellets is a traditional method in faunistic studies to provide data on distribution of small mammals, especially cryptic species which are hard to be found using trapping. Here, we present a dataset on mammals found in Tawny owl pellets collected during up to 13-year studies in the Kharkiv Region, Ukraine in three territories. Data from two territories were collected in a systematic way and allowed us to make analysis of seasonal, year-to-year and habitat variability in the Tawny owl diet and local mammal species composition.